As global environment problems occur, fossil energy is exhausted and problems relating to disposal of waste in nuclear power generation and determination of sites of new power generation plants occur, new renewable energy has drawn attention, and research and development of generation of solar light that is a pollution-free energy source among new renewable energy have been briskly conducted in domestic and foreign countries.
Solar cells are optical devices that receive light energy from incident light and convert light energy into electrical energy by using a photoelectromotive force. Research for improving light generation efficiency and research for reducing manufacturing cost have been conducted. In order to improve light generation efficiency, tandem type solar cells that absorb solar light having a long wavelength and solar light having a short wavelength efficiently have been widely studied. In addition, in order to reduce manufacturing cost, organic-inorganic composite materials that are used in existing silicon-based solar cells have been widely studied.
Tandem type solar cells that absorb solar light in a wide wavelength region efficiently can overcome a limitation in light generation efficiency of solar cells having a single energy bandgap. However, due to characteristics of a device that is called a stacked multilayered structure, losses of light generation efficiency occur when solar light is transmitted through a thin layer. The greatest loss among the losses is a loss of defects caused by lattice mismatch that occurs in a tunnel junction portion between heterojunction thin layers and crystalline defects of thin layers. In particular, when a photoelectric conversion layer is formed in a lower portion of a solar cell, the amount of transmitted light energy is reduced, and thus light generation efficiency is rapidly lowered. In addition, since semiconductor thin layers having good crystallinity should be stacked in a multilayered structure in order to reduce light loss, an epitaxial deposition method with high processing cost and a long processing time needs to be used. For this reason, manufacturing cost increases so as to absorb solar light in a wide wavelength region efficiently, and a limitation in light generation efficiency occurs.
In order to reduce manufacturing cost of tandem type solar cells, solar cells using organic-inorganic composite materials have been also studied. However, tandem type tandem type solar cells using organic-inorganic composite materials can use inexpensive organic materials, but light loss occurs between stacked thin layers, and light generation efficiency is rapidly lowered due to defects of organic thin layers and defects between organic and inorganic thin layers.
Thus, a new concept of solar cells that may reduce manufacturing cost and simultaneously may prevent light generation efficiency from being rapidly lowered due to light loss, are required.